1. Field of the Invention
The present invention relates to a liquid container (hereinafter referred to also as ink tank) for use in a recording apparatus which forms an image by discharging a recording agent such as ink. The present invention can be applied to a recording apparatus in general, and other apparatus such as a copying machine, a facsimile which has a communication system, a word processor which has a printing unit, or an industrial recording apparatus which is multiply combined with various processing apparatuses.
1. Description of the Related Art
An ink jet recording apparatus includes a recording head, an ink tank which is connected to the recording head and supplies ink to the recording head, and a carriage on which the recording head can be mounted. In order to record an image, ink droplets are discharged from a microscopic discharge port on the recording head in accordance with image data while the carriage is moved relative to the recording medium. These ink droplets are applied onto the recording medium to form the desired image.
Conventionally, in an ink jet recording apparatus as above described, ink containing dye (hereinafter referred to as dye ink) is mainly used as the color material. However, dye ink generally has problems in terms of light resistance and gas resistance, and there are cases where recorded images using dye ink cannot provide sufficient image robustness for outside display.
In order to deal with such problems, recording apparatuses which use ink containing pigment (hereinafter referred to as pigment ink) as the color material are already in the market. Pigments excel in light resistance and gas resistance, and recorded images using this type of ink show sufficient image robustness. However, as compared to the dye ink, the pigment ink has various problems in terms of handling. One example of such problems is the dispersibility of the color material within the ink.
Unlike the dye molecules, the pigment molecules do not dissolve into the ink solution, and the molecules float in a dispersed state. Therefore, when the ink tank is left at rest for some time, the pigment particles within the ink tank gradually settle out by gravitation, which causes a density inclination of the pigment particles heightwise in the ink tank. That is, at the bottom part of the ink tank, a layer is formed in which the density of the color material is high, and a low-concentration layer is formed at the upper part of the ink tank. If recording is started or continued in this state, a density difference appears between images outputted at an early stage and at a later stage of the usage of the ink tank.
More specifically, in an ink jet recording apparatus, the ink is supplied to the recording head from the bottom part of the ink tank. In this case, when an ink tank with a density inclination as above described is mounted on the apparatus, ink is supplied from the lower layer with a high density of color material at the start of the recording. As a result, an image with an excessively high density is outputted. As the number of recorded sheets of paper increases and the ink inside the ink tank is consumed, the density of the image gradually becomes lower. When the amount of ink in the ink tank becomes very little, only the ink with lower density of the color material as compared to the initial density is remaining. Therefore, the recorded object will show an insufficient density although it is recorded according to the same image data as at the beginning of the recording. In particular, there is a significant settling-out of the pigment particles in the case where the diameter or the specific gravity of the particle is large, and a density inclination large enough to have an effect on the image is generated only when the ink tank has not been used for several continuous days.
The above-described problem in that the density of the color material in the discharged ink fluctuates as the ink tank is being used, does not only generate a density difference between the images outputted at the beginning stage and the later stage of the color tank usage. A color ink jet recording system uses a plurality of color inks to express the desired hue based on a predetermined color balance. In the color ink jet recording system, the above problem can lead to the color imbalance, and becomes a more noticeable image issue.
To overcome the above problem, the density of the color material in the ink droplet discharged from the recording head is required to be maintained within a desired range independent of the amount of ink remaining in the ink tank. In order to realize this, it is desirable that the pigment molecules are dispersed evenly in the ink tank, at least during the recording.
In order to realize the even dispersion, an agitating member has been proposed which agitates the pigment molecules inside the ink tank (for examples, refer to Japanese Patent Application Laid-Open No. 2005-066520 and Japanese Patent Application Laid-Open No. 2004-216761.).
More specifically, Japanese Patent Application Laid-Open No. 2005-066520 discusses an ink pack (or tank) having an agitating member which can be operated manually according to the first and second exemplary embodiments. In this reference, the agitating member is inserted from the outside into the ink pack or the ink tank. The section of the agitating member which is externally protruding, acts as the operating section for moving the agitating section inside the ink pack (or tank). Both embodiments teach that the user oscillates the agitating section regularly or, as required, to directly agitate the ink inside the ink pack (or the ink tank) so that the pigment molecules can be dispersed.
The third exemplary embodiment of Japanese Patent Application Laid-Open No. 2005-066520 discusses an ink tank having an agitating member which agitates the ink inside the tank exerting the inertial force when the carriage moves in the recording process. As one example, an agitating member which is formed integrally with the ink tank case is discussed. The agitating member is extended hanging from the ceiling to the bottom part of the ink tank case, and a cylindrical spindle is formed at the bottom end of the agitating member. By the inertial force accompanying the acceleration, termination, and reverse movement of the carriage scanning, the agitating member oscillates in the scanning direction of the carriage with the base part fixed at the ceiling as the fulcrum and agitates the ink inside the tank.
Japanese Patent Application Laid-Open No. 2005-066520 discusses another example of an agitating member which is not fixed to the ink tank case and can move freely along the bottom surface of the ink tank. The agitating member moves along the bottom surface of the tank with an inertial force generated by the acceleration, termination, and reverse movement of the carriage scanning, and agitates the ink.
Furthermore, Japanese Patent Application Laid-Open No. 2004-216761 discusses an agitating mechanism having an axial spindle which oscillates from side to side centering the oscillation axis driven by the inertial force, and a plurality of fins formed together with the axial spindle which also oscillate from side to side, in accordance with the movement of the carriage. In this configuration, since the plurality of fins is arranged in parallel heightwise in the ink tank, the ink can be agitated evenly from the upper part to the lower part within the tank.
However, in order to constantly obtain a favorable dispersibility of the pigment particles, the agitation effect is not sufficient in both of the above references.
For example, in the first and second exemplary embodiments of Japanese Patent Application Laid-Open No. 2005-066520, since movement of the manually-operated agitating member is limited, only a limited area within the tank can be agitated. In particular, in the vicinity of the joining section between the agitating member and the ink tank which acts as the fulcrum, the area where the agitating member can move, is very narrow, and sufficient agitation cannot be achieved.
Besides, in the third exemplary embodiment of Japanese Patent Application Laid-Open No. 2005-066520, the area which can be agitated, is not sufficient although the inertial force is used efficiently. For example, in the case where the agitating member is formed integrally with the tank, the agitation in the vicinity of the fulcrum can be also insufficient. Furthermore, in the case of the agitating member that can move freely along the bottom surface of the ink tank, the upper part of the ink tank that is away from the agitating member, can not be expected to be well agitated as in the vicinity of the bottom part.
In contrast, a plurality of fins are arranged heightwise in the ink tank in the configuration discussed in Japanese Application Laid-Open No. 2004-216761 so that a heightwise uniform agitation can be expected to some extent. However, since the quantity of turning of the fins is small near the central shaft inside the tank, the agitation effect is small in that portion. Furthermore, the configuration of an agitation member having such plurality of fins or a rotating shaft is complex and the ink tank itself becomes expensive.
Originally, in an ink jet recording apparatus which mounts an ink tank on the carriage and records images, the width of the ink tank relative to the main scanning direction is designed to be narrow in order to avoid the apparatus from becoming large. Therefore, even in the case where an agitating member is provided inside the ink tank and the inertial force of the carriage movement is utilized, the amount of displacement in the main scanning direction is limited. Therefore, how to efficiently agitate all of the ink remaining inside the tank using the limited amount of displacement becomes the significant issue in the configuration of the agitating member. In the case where an image is recorded using an ink tank which has been laid at rest for a long time, an agitation such as the carriage oscillation must be performed before the recording. If this agitation is not performed efficiently, much time will be required for the warm-up process.